Unit 4: Momentum

Momentum and Impulse Section 4-1

Lesson Objectives • Calculate mass, velocity, or momentum given the other two quantities. • Describe impulse and how it relates to momentum. • Solve problems involving impulse. • Analyze and compare the momentum and impulse of different objects.

Momentum • The momentum of an object is equal to its mass times its velocity • Is represented by a lower case “” • Is a vector (has magnitude and direction) • Has units of kg· m/s – Equivalent to N· s

Think-Pair-Share • Which of the following has the most momentum? The least momentum? a) A parked 18-wheeler truck b) A baseball immediately after it is hit c) A proton in the Large Hadron Collider (LHC) traveling near the speed of light d) A charging rhinoceros

Momentum Equation

= = =

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Think-Pair-Share • Momentum is ______________ proportional to mass.

You-Try #1 • Suppose a truck has a momentum of kg∙m 42,825 north and a mass of 1250 kg. s What is the truck’s velocity?

• Momentum is ______________ proportional to velocity.

You-Try #2 • Suppose a 1380 kg speedboat is traveling east at 14.2 m/s. What is the speedboat’s momentum?

Think-Pair-Share • Order the following from least momentum to greatest momentum: A. = 0.45 kg, = 25 m/s B. = 0.45 kg, = 15 m/s C. = 0.45 kg, = 50 m/s D. = 0.45 kg, = 0 m/s E. = 0.45 kg, = 40 m/s

You-Try #3 • A 4825 charging rhinoceros has a momentum kg∙m of 6.90 × 10 s south. What is the rhino’s velocity?

Impulse • The impulse acting on an object is equal to the force acting on it multiplied by the time interval over which it acts • Is represented by a capital “” • Is a vector (has magnitude and direction) • Has units of N· s – Equivalent to kg∙m/s

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Impulse Equation

= Δ

You-Try #4 • A volleyball player’s hand applies a 52.0 N force upward while in contact with a volleyball for 0.825 s. What is the impulse on the ball?

Δ Δ = =

Newton’s Second Law, again = Δ = Δ Δ = Δ Assuming constant mass: Δ = Δ = Δ

Example 5 • A baseball has a mass of 0.145 kg. A pitcher throws it with a velocity of − 41.3 m/s. The bat hits the ball with a force of 130. N for 0.100 seconds. What is the ball’s velocity after it leaves the bat?

Impulse-Momentum Theorem • The net impulse acting on an object is equal to the object’s change in momentum = Δ

Δ = − "

You-Try #5 • A hockey puck has a mass of 0.115 kg. A player hits it towards the goal with a velocity of − 28.7 m/s. The puck misses the goal, and instead hits the goalpost with a force of 73.6 N for 0.0700 seconds. What is the puck’s rebound velocity?

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Think-Pair-Share • Explain, using the physics terms and equations from this section, the purpose of a car’s airbags.

Collisions • For a set initial and final velocity, the change in momentum is constant. • Increasing the collision time will decrease the magnitude of the force. • Decreasing the collision time will increase the magnitude of the force.

Assignment • Read Textbook chapter 7 • Textbook page 100 #1-12, 19-21, 24 • 4-1 Practice Problems

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